Electric Actuator

Abstract

An electric actuator 20 is provided. The actuator 20 comprises an electric drive means 22 and a drive member 26 that is rotationally driven when the electric drive means 22 is actuated, an output member 24 that is rotationally connected to the drive member 26 by a first spring 28, and a second spring 32 that is connected to the output member 24 and forms a one-way clutch between the output member 24 and a fixed tube 34, and the electric actuator 20 further comprises an adjusting cup 30 configured to engage the second spring 32 to decouple the output member 24 from the fixed tube 34. [Selected Figure] Figure 2

Description

[Technical field]

[0001] The present invention relates to electric actuators used in automotive applications, and more particularly to latching mechanisms for such electric actuators. [Background technology]

[0002] A vehicle typically includes several pairs of rotating members that must be selectively connected to one another to enable a desired torque transfer between the respective members. For example, such members may be input and output drive shafts, or the output shaft of an electric motor and associated drive train members.

[0003] The selective torque transfer between two rotating members is usually regulated by a clutch and suitable control of such a clutch, for example a disc clutch or a dog clutch, one side of which is connected to a rotating input shaft and the other side of which is connected to an output shaft, such that closing of the clutch urges the output shaft to rotate with the rotating input shaft.

[0004] Clutch control requires an actuator. There are many different types on the market, but electric actuators are increasingly in demand. Electric actuators usually work against elasticity. In the case of dog clutches, the elasticity is provided by a return spring that biases the dog clutch towards the disengaged mode, while in the case of disc clutches, the elasticity is provided by the inherent bias of the individual discs. The elasticity ensures that there is no torque transmission when the drive current is zero. This arrangement is for safety reasons, preventing unintended lock-up of the clutch. On the other hand, the elasticity during clutch activation must be countered, which requires that the actuator must be supplied with a high current during steady torque transmission.

[0005] It is desirable to lower the steady-state holding torque of an electric actuator while keeping the holding torque at zero in the absence of drive current in order to reduce power consumption and also to protect the electric actuator from overheating. Thus, an improved electric actuator is needed. Summary of the Invention [Problem to be solved by the invention]

[0006] It is an object to provide an improved electric actuator that can alleviate some of the problems of the prior art, and to provide an electric actuator that provides desired operational functionality in a simple, robust, reliable and cost-effective manner. [Means for solving the problem]

[0007] According to a first aspect, there is provided an electric actuator comprising: an electric drive means and a drive member which is rotationally driven upon actuation of the electric drive means; an output member rotationally connected to the drive member by a first one-way spring clutch; and a second spring connected to the output member and forming a one-way clutch between the output member and a fixed tube forming part of a fixed housing. The electric actuator further comprises an adjusting cup configured to engage the second spring to decouple the output member from the fixed tube.

[0008] The drive member and the output member may be arranged coaxially.

[0009] The regulating cup may surround the drive member as well as the output member.

[0010] A first end of the first spring may be secured to the output member and a second end of the second spring may be secured to the drive member as well as the adjusting cup.

[0011] The second spring may be maneuverable between an idle position, in which the output member is connected to the fixed tube, and an open position, in which the output member is disconnected from the fixed tube.

[0012] The first spring may be configured to provide automatic return rotation of the output member when the second spring maneuver to its open position.

[0013] The adjustment cup may have a circular end at an axial location of the radially protruding end of the second spring and at least one axial edge configured to press against the end of the second spring upon rotation of the adjustment cup.

[0014] The axial edge of the rounded end may be formed by an interface between an axially longer portion of the rounded end and an axially shorter portion of the rounded end.

[0015] According to a second aspect, there is provided a clutch comprising an electric actuator according to the first aspect.

[0016] The clutch may have elastic properties resulting from a return bias function of the clutch.

[0017] According to a third aspect, there is provided a vehicle comprising at least one clutch according to the second aspect.

[0018] The invention is explained in further detail below with reference to the accompanying drawings. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram of a vehicle according to one embodiment. [Diagram 2] FIG. 2 is a cross-sectional view of an electric actuator according to one embodiment. [Diagram 3] FIG. 3 is an isometric view of the components of the electric actuator shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] In FIG. 1, a vehicle 1 is shown diagrammatically. The vehicle 1 has a front axle 3, a rear axle 5 and a propulsion unit 7 connected to the front axle 3, the rear axle 5 or both. The vehicle 1 is provided with one or more clutches 9a-9b. In the example shown, a first clutch 9a is arranged on the rear axle 5 to enable all-wheel drive of the vehicle 1. The first clutch 9a is for this purpose a disk clutch 9a arranged in the rear axle differential 11, by actuating the disk clutch 9a, the rear axle 5 receives a driving torque from the propulsion unit 7.

[0021] The vehicle 1 in the example shown also comprises a second clutch 9b, here in the form of a dog clutch 9b located on the front axle 3 and decoupling the rear axle 5 (and cardan shaft 13) from the drive train. When operating in two-wheel drive mode, the dog clutch 9b is disengaged, thereby reducing the rotating mass of the vehicle 1. When four-wheel drive mode is required, the disc clutch 9a is actuated to rotate the cardan shaft 13, after which the dog clutch 9b is actuated to connect the rear axle 5 (via the dog clutch 9b and the disc clutch 9a) to the propulsion unit 7.

[0022] The at least one clutch 9a-9b is modulated by an actuator 20, which will be further described below. However, before moving to details of the electric actuator 20, it should be noted that the exact configuration of the vehicle 1 shown in FIG. 1 is for illustrative purposes only. It should be readily understood that the vehicle 1 could have in principle any possible configuration, so long as there is at least one electric actuator 20 arranged in combination with any suitable clutch 9a-9b. Such examples include a transfer case, an electric drivetrain, a torque vectoring system, etc.

[0023] An embodiment of an electric actuator 20 is shown in FIG. 2. The electric actuator 20 comprises an electric drive means 22, for example a DC motor, a brushless DC motor or a rotary solenoid. The electric actuator 20 also has an output member 24 connected to a clutch (not shown) via any suitable connection or gearing. As explained before, the clutch can be, for example, a dog clutch 9b or a disk clutch 9a. Importantly, the associated clutches 9a-9b form an elastic system. That is, the clutches 9a-9b are provided with a return bias function such that the output member 24 is subjected to a return force, as will be explained further below. Preferably, the clutch is configured such that the rotation of the output member 24 controls the actuation of the clutch.

[0024] The electric drive means 22 is connected to a drive member 26 arranged to rotate upon actuation of the electric drive means 22. With reference to the output member 24, the drive member 26 forms an input shaft. The drive member 26 is connected to the output member 24 by a return rotation spring 28 forming a one-way clutch. The drive member 26 and the output member 24 are arranged coaxially, with their axial ends facing each other. The return rotation spring 28 is arranged around the outer circumference of the drive member 26 and the output member 24. One end 28a of the return rotation spring 28 is fixed to the output member 24, for example by inserting the end 28a into a radial hole drilled in the output member 24. The opposite end 28b of the return rotation spring 28 is rigidly attached to the drive member 26 and to an adjusting cup 30 connected thereto. The adjusting cup 30 is thus rotationally fixed to the drive member 26.

[0025] When the electric drive means 22 is actuated, it rotates the drive member 26 and therefore also the return spring 28. As one end 28a of the return spring 28 is fixed to the output member 24, the diameter of the return spring 28 decreases until it comes into contact with the outer surfaces of the drive member 26 and the output member 28. As a result, rotation of the output member 24 is achieved. This rotational movement of the output member 24 corresponds to the actuation of an associated clutch, for example by compressing a spring or by squeezing disks towards each other.

[0026] The output member 24 is also provided on its outer periphery with a spring which forms a one-way spring clutch 32. For this purpose, the output member 24 has a radial extension 25 in which the spring 32 is arranged, so that the spring 32 is arranged in a different radial and axial position compared to the return rotation spring 28.

[0027] One end 32a of the spring 32 is rotationally fixed to the output member 24, for example by inserting the end 32a into a drilled radial hole. The spring 32 is clamped around a fixed tube 34, which forms part of a fixed housing 36. Thus, when the electric drive means 22 is actuated, the rotation of the output member 24 also enables the spring 32 to rotate around the fixed tube 34.

[0028] When the desired rotation of the output member 24 is reached, i.e. when the associated clutch 9a-9b has been actuated in the desired manner, the current supplied to the electric drive means 22 is significantly reduced, for example to a level of 5-25%, preferably 10%, compared to the current required during actuation. This corresponds to the so-called holding position, in which the output member 24 of the actuator 20 is intended to hold its position obtained by the rotation of the drive member 26. This current is sufficient to drive the electric drive means 22 to maintain the drive member 26 in a given position, while the provision of the spring 32 prevents an automatic return movement of the output member 24. This is due to the fact that the friction between the spring 32 and the fixed tube 34 prevents an automatic return rotation of the output member 24 relative to the fixed tube 34, whereby the spring 32 accommodates the torque through the fixed tube 34.

[0029] Once the actuation is completed, the drive current is interrupted, so that the torque provided by the electric drive means 22 becomes zero. The return rotation spring 28 can then rotate the drive member 26 and the electric drive means 22 backwards, which also causes a corresponding rotational movement of the regulating cup 30. The regulating cup 30 surrounds the drive member 26 as well as the output member 24, and extends as a sleeve surrounding these two members 24, 26. As already mentioned, one end 30a of the regulating cup 30 is rotationally fixed to the drive member 26. The opposite end 30b has a circular shape, as shown in FIG. 3. This circular end 30b has a part of its circumference cut axially, so that a first part 30c of the periphery of this end 30b has a somewhat longer axial length than another part 30d of the periphery. The two parts 30c-30d are arranged adjacent to each other and together form a total circular periphery, which means that two axial edges 30e are formed at the interface between the two parts 30c-30d. The axial length and diameter of the circular end 30b of the adjusting cup 30 are dimensioned such that the axial end 30e can come into contact with the radially protruding end 32b of the spring 32.

[0030] As the adjusting cup 30 rotates backwards, the axial end 30e eventually contacts and pushes against the radial end 32b of the spring 32, releasing its clutch function, thereby causing the output member 24 to rotate backwards.

[0031] The embodiments described herein enable a very simple, yet robust and reliable electric actuator that enables i) automatic return movement of the output member 24 when the drive current is zero, and ii) significantly reduced drive current required to hold the output member 24 in its actuated position.

Claims

1. an electric actuator (20) comprising an electric drive means (22) and a drive member (26) which are rotationally driven upon actuation of the electric drive means (22); an output member (24) rotationally connected to the drive member (26) by a first one-way spring clutch (28); and a second spring (32) connected to the output member (24) and forming a one-way clutch between the output member (24) and a fixed tube (34) which forms part of a fixed housing, the electric actuator (20) further comprising an adjusting cup (30) rotationally connected to said drive member (26) and configured to engage the second spring (32) to decouple the output member (24) from the fixed tube (34); The second spring (32) is operable between an idle position in which the output member (24) is connected to the fixed tube (34) and an open position in which the output member (24) is disconnected from the fixed tube (34).

2. The electric actuator (20) of claim 1, wherein the drive member (26) and the output member (24) are coaxially disposed.

3. The electric actuator (20) of claim 1 or 2, wherein the regulating cup (30) surrounds the drive member (26) as well as the output member (24).

4. The electric actuator (20) of any one of claims 1 to 3, wherein a first end (28a) of a first spring (28) is fixed to the output member (24) and a second end (28b) of the first spring (28) is fixed to the drive member (26) as well as to the adjusting cup (30).

5. the first spring (28) is configured to provide automatic return rotation of said output member (24) when the second spring (32) is operated to its open position; The automatic return rotation is such that, when the torque supplied by the electric drive means (22) becomes zero, the first spring (28) can rotate the drive member (26) and the electric drive means (22) in a direction opposite to the forward rotation direction, the adjusting cup (30) also rotates in a direction opposite to the forward rotation direction, and the axial end (30e) finally contacts and pushes against the radial end (32b) of the second spring (32) to release the clutch function, and the output member (24) automatically rotates in the direction opposite to the forward rotation direction.

6. The electric actuator (20) according to any one of claims 1 to 5, wherein the adjusting cup (30) has a circular end (30b) at the axial location of the radially protruding end (32b) of the second spring (32) and at least one axial edge (30e) configured to press against the end (32b) of the second spring (32) upon rotation of the adjusting cup (30).

7. an axial edge (30e) of the circular end (30b) is formed by the interface between an axially longer portion (30c) of the circular end (30b) and an axially shorter portion (30d) of the circular end (30b); 7. The electric actuator (20) of claim 6, wherein the circular end (30b) is cut axially along a portion of its circumference such that a first portion (30c) and a second portion (30d) together form the axial edge (30e), the first portion (30c) having a greater axial length than the second portion (30d).

8. A clutch (9a-9b) comprising an electric actuator (20) according to any one of the preceding claims.

9. A clutch (9a-9b) according to claim 8, wherein the clutch (9a-9b) is provided with elastic properties resulting from a return bias function of the clutch (9a-9b).

10. A vehicle (1) comprising at least one clutch (9a-9b) according to claim 8 or 9.

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